The field of the present invention is control systems for turbines, and more particularly, systems for preventing turbine overspeed upon loss of load.
In fluid driven turbines used for generating electrically or for performing other work, sudden load loss during normal operation is not uncommon. Should such load loss occur, the turbine, if unchecked, can quickly reach a destructive overspeed condition. To resolve this problem, it has been suggested to place an emergency control valve between the fluid source and the turbine inlet. The valve, in response to a turbine overspeed condition indicating loss of load, will immediately close to interrupt the flow of fluid to the turbine, thus resulting in complete turbine shutdown.
Although basically effective, such valves may not be satisfactory for all loading applications. For example, many turbines are utilized to drive primary and secondary load groups. Should the primary load group be lost, complete shutdown is undesirable. Rather, the turbine should continue to power the remaining secondary load group. Thus, a control system is needed for turbines driving multiple load groups that would prevent destructive turbine overspeed upon loss of one load group but which would allow the turbine to continue to drive the remaining load group(s).